Study Of Fire Resistance Of Self-stressing Lightweight Aggregate Concrete Filled Steel Tubular Columns

Concrete filled steel tube (CFST) is widely used for its higher bearing capacity, fineplasticity and toughness and so on. Compared with ordinary concrete filled steel tubes (CFST),Self-stressing lightweight aggregate concrete filled steel tubes (SLCFST) has characteristic oflight weight, better restraint of steel tube to core concrete and so on. Therefore, the research onthis topic not only has important theoretical significance but also has wide practical application.However, the research on long columns of SLCFST is relatively few in academic circlecurrently, and the study about its fire-resistance property is even a blank. With the object ofreduced scale of long columns of self-stressing lightweight aggregate concrete filled steel, andthis article focuses their fire resistance of the experimental study. The main research contentsare listed as follows:Firstly, effect of mixing amount of expansive agent and steel ratio on expansive propertywas investigated through test of self-stress of nine self-stressing lightweight aggregate concretefilled steel tubes. Secondly, the mechanical behavior and the fire-resistance behavior wereexperimentally studied on ten SLCFST not subjected to fire load, twenty SLCFST under fireand eighteen SLCFST after exposure to fire, respectively, in which the parameters such as steelratio, mixing amount of expansive agent and external loads were considered. Finally, areasonable model was selected and axial bearing property of post-fire SLCFST was simulatedby FEM software ANSYS, and the influence of steel ratio on the axial compressive bearingcapacity of post-fire SLCFST was further discussed.The following conclusions can be obtained from this research:(1)The restraint of steeltube to core concrete increased with the mixing amount of expansive agent and steel ratio;(2)The ultimate bearing capacity of SLCFST after exposure to fire and that not subjected to fireload can be improved by steel ratio;(3)The larger axial compression under fire is, the largerultimate bearing capacity of SLCFST after exposure to fire is instead, but this trend weakenwith the steel ratio increases;(4)For the specimens with the same mixing amount of expansiveagent and external loads under fire, the residual bearing capacity influence coefficient of thespecimens increases with steel ratio;(5)The simulation results of axial compression bearingcapacity of part of SLCFST after exposure to fire presented here are well identical to the experimental results;(6) The variables of self-stress level was used to obtain the formula ofaxial compression bearing capacity of long columns of SLCFST based on the method ofcalculation of ordinary concrete filled steel tubes (CFST).